Use of global positioning satellite (GPS) receivers in automotive navigation, emergency messaging, and tracking systems is now widespread. However, systems based solely on GPS generally do not work well in dense city environments, where signal blockage and reflection by tall buildings, in addition to radio frequency interference, often occurs. A cost effective solution to this problem is to augment the GPS receiver with some form of Dead Reckoning (DR), to fill in the gaps occurring as a result of loss of GPS coverage and improve the accuracy of the GPS trajectory.
A DR system commonly takes the form of an interface to the transmission odometer of the vehicle to provide an indication of speed, in combination with a low cost gyro to track the vehicle's heading. This odometer interface makes the DR system installation unique to each vehicle type, and so is undesirable for many potential applications. Thus, a conventional DR system requires a "customization" to each alternative vehicle type.
Accordingly, the present invention extends GPS coverage in an automotive environment without requiring direct interfaces to the vehicle's sensors in a unique and very cost effective way. Since it removes all required vehicle interfaces except power, it produces a virtually portable navigation system with no installation requirements beyond that of the GPS receiver itself. It also removes the necessary "customization" of the navigation system to each particular vehicle. Fundamentally, the GPS receiver is augmented with a low cost gyro, which accurately tracks the heading changes of the vehicle (in the absence of GPS), and an innovative algorithm for deriving speed information from Doppler measurements from just one or two GPS satellites combined with the vehicle heading predicted from the low cost gyro.